Add maintenance note

Author: perliedman

README.md

@@ -1,6 +1,8 @@
 [Leaflet Routing Machine]((https://www.liedman.net/leaflet-routing-machine/)) [![NPM version](https://img.shields.io/npm/v/leaflet-routing-machine.svg)](https://www.npmjs.com/package/leaflet-routing-machine) ![Leaflet 1.0 compatible!](https://img.shields.io/badge/Leaflet%201.0-%E2%9C%93-1EB300.svg?style=flat) [![Join the chat at https://gitter.im/leaflet-routing-machine/Lobby](https://badges.gitter.im/leaflet-routing-machine/Lobby.svg)](https://gitter.im/leaflet-routing-machine/Lobby?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
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+**This plugin is barely maintained!** It has been a good long while since I had any reason to work with routing or Leaflet, and it does not look like that will change. I do not spend time on maintaining this plugin, and only rarely can I find time to respond to issues. If you want to take over as maintainer, feel free to contact me at [email protected].
+
 Find the way from A to B on a Leaflet map. The plugin supports multiple backends:
 
 * [OSRM](http://project-osrm.org/) - builtin and used by default (version 5)